Boxer - 8:36 am on Mar 1, 2011 (gmt 0)
J_RaD -> It started when I updated to Plesk 10+ (latest version)
I am not sure if that was the problem.
mbabuskov -> There was a slight slowdown.
I changed the server OS, now running Debian instead of Centos.
Everything is running fine now.
Thanks for your help.